Proper queueing of external events and sample APZ when building the s…

…cene.

webrender/src/render_backend.rs

@@ -206,6 +206,9 @@ impl Document {
                 };
             }
             FrameMsg::HitTest(pipeline_id, point, flags, tx) => {
+                if !self.hit_tester_is_valid {
+                    self.rebuild_hit_tester();
+                }
 
                 let result = match self.hit_tester {
                     Some(ref hit_tester) => {
@@ -640,6 +643,9 @@ impl RenderBackend {
                     SceneBuilderResult::FlushComplete(tx) => {
                         tx.send(()).ok();
                     }
+                    SceneBuilderResult::ExternalEvent(evt) => {
+                        self.notifier.external_event(evt);
+                    }
                     SceneBuilderResult::Stopped => {
                         panic!("We haven't sent a Stop yet, how did we get a Stopped back?");
                     }
@@ -742,7 +748,7 @@ impl RenderBackend {
                 ).unwrap();
             }
             ApiMsg::ExternalEvent(evt) => {
-                self.notifier.external_event(evt);
+                self.low_priority_scene_tx.send(SceneBuilderRequest::ExternalEvent(evt)).unwrap();
             }
             ApiMsg::ClearNamespace(namespace_id) => {
                 self.resource_cache.clear_namespace(namespace_id);
@@ -984,7 +990,7 @@ impl RenderBackend {
         // fiddle with things after a potentially long scene build, but just
         // before rendering. This is useful for rendering with the latest
         // async transforms.
-        if requested_frame {
+        if requested_frame || has_built_scene {
             if let Some(ref sampler) = self.sampler {
                 frame_ops.append(&mut sampler.sample());
             }

webrender/src/scene_builder.rs

@@ -3,7 +3,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 use api::{AsyncBlobImageRasterizer, BlobImageRequest, BlobImageParams, BlobImageResult};
-use api::{DocumentId, PipelineId, ApiMsg, FrameMsg, ResourceUpdate, Epoch};
+use api::{DocumentId, PipelineId, ApiMsg, FrameMsg, ResourceUpdate, ExternalEvent, Epoch};
 use api::{BuiltDisplayList, ColorF, LayoutSize, NotificationRequest, Checkpoint};
 use api::channel::MsgSender;
 #[cfg(feature = "capture")]
@@ -114,6 +114,7 @@ pub struct BuiltScene {
 // Message from render backend to scene builder.
 pub enum SceneBuilderRequest {
     Transaction(Box<Transaction>),
+    ExternalEvent(ExternalEvent),
     DeleteDocument(DocumentId),
     WakeUp,
     Flush(MsgSender<()>),
@@ -130,6 +131,7 @@ pub enum SceneBuilderRequest {
 // Message from scene builder to render backend.
 pub enum SceneBuilderResult {
     Transaction(Box<BuiltTransaction>, Option<Sender<SceneSwapResult>>),
+    ExternalEvent(ExternalEvent),
     FlushComplete(MsgSender<()>),
     Stopped,
 }
@@ -226,6 +228,10 @@ impl SceneBuilder {
                 Ok(SceneBuilderRequest::SaveScene(config)) => {
                     self.save_scene(config);
                 }
+                Ok(SceneBuilderRequest::ExternalEvent(evt)) => {
+                    self.tx.send(SceneBuilderResult::ExternalEvent(evt)).unwrap();
+                    self.api_tx.send(ApiMsg::WakeUp).unwrap();
+                }
                 Ok(SceneBuilderRequest::Stop) => {
                     self.tx.send(SceneBuilderResult::Stopped).unwrap();
                     // We don't need to send a WakeUp to api_tx because we only